Understanding Millennial-scale Shifts in Australian Monsoon Variability Over the Past 40,000 Years Through Analysis of Stable Isotopes in Calcite Stalagmites

Approximately one third of the global population lives in the area affected by the Indo-Australian monsoon. Understanding the variability and dynamics of Australian monsoon rainfall, especially in response to global climate change, is of critical importance. Research in Borneo and Indonesia has demonstrated that the strength of the Indo-Australian monsoon is tied to millennial-scale climate anomalies originating in the North Atlantic. In particular, changes in thermohaline circulation of the world’s oceans during Heinrich events—one to two thousand-year-long episodes of cooling caused by the influx of large amounts of freshwater into the North Atlantic—that influence global climate and produce signals that can be tracked in paleoclimate records around the world. But little is understood about the response of the Indo-Australian monsoon to these events over mainland Australia. Here we present high-resolution uranium-thorium dates of stalagmites from Ballgown cave, Windjana Gorge, located in tropical Western Australia. Oxygen and carbon stable isotope values in calcite stalagmites can be used as paleoclimate proxies when properly dated. By resolving the growth time-series using uranium/thorium dating, we can correlate global climate trends from other records of the past 40,000 years to trends in the stable isotope data from the stalagmites and reconstruct past monsoon variability in the region. This will help us further understand the climate processes that drive the modern Indo-Australian monsoon system.

Approximately one third of the global population lives in the area affected by the Indo-Australian monsoon. Understanding the variability and dynamics of Australian monsoon rainfall, especially in response to global climate change, is of critical importance. Research in Borneo and Indonesia has demonstrated that the strength of the Indo-Australian monsoon is tied to millennial-scale climate anomalies originating in the North Atlantic. In particular, changes in thermohaline circulation of the world’s oceans during Heinrich events—one to two thousand-year-long episodes of cooling caused by the influx of large amounts of freshwater into the North Atlantic—that influence global climate and produce signals that can be tracked in paleoclimate records around the world. But little is understood about the response of the Indo-Australian monsoon to these events over mainland Australia. Here we present high-resolution uranium-thorium dates of stalagmites from Ballgown cave, Windjana Gorge, located in tropical Western Australia. Oxygen and carbon stable isotope values in calcite stalagmites can be used as paleoclimate proxies when properly dated. By resolving the growth time-series using uranium/thorium dating, we can correlate global climate trends from other records of the past 40,000 years to trends in the stable isotope data from the stalagmites and reconstruct past monsoon variability in the region. This will help us further understand the climate processes that drive the modern Indo-Australian monsoon system.